feat(firefox): support mobile mode

[Andrey Lushnikov (aslushnikov)]

note: this requires Juggler's support for the mobile mode first.

Fixes #39841

[github-actions]

Test results for "MCP"

1 failed
❌ [chrome] › mcp/dashboard.spec.ts:54 › should show one row per context for a single browser @mcp-windows-latest-chrome

7265 passed, 1119 skipped

---

Merge workflow run.

[github-actions]

Test results for "tests 1"

7 flaky

⚠️ [chromium-library] › library/popup.spec.ts:261 › should not throw when click closes popup `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/video.spec.ts:275 › screencast › should capture navigation `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/video.spec.ts:717 › screencast › should work with video+trace `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/browsertype-connect.spec.ts:938 › run-server › socks proxy › should proxy requests from fetch api `@chromium-ubuntu-22.04-node24`
⚠️ [chromium-library] › library/video.spec.ts:275 › screencast › should capture navigation `@chromium-ubuntu-22.04-node24`
⚠️ [chromium-library] › library/chromium/chromium.spec.ts:299 › should report intercepted service worker requests in HAR `@chromium-ubuntu-22.04-node20`
⚠️ [chromium-library] › library/popup.spec.ts:261 › should not throw when click closes popup `@chromium-ubuntu-22.04-node20`

39506 passed, 771 skipped

---

Merge workflow run.